1. Field of the Invention
The present invention relates to a projector apparatus for displaying an enlarged computer image or video image.
2. Related Background Art
In recent years, image display apparatuses such as liquid crystal projectors are required to improve brightness. FIG. 15 shows the arrangement of a conventional projecting image display apparatus (projector apparatus).
Referring to FIG. 15, white light emitted from a light source section 101 of an ultrahigh-pressure mercury-vapor lamp is reflected by a reflector 102 and transmitted through fly-eye lenses 103 and 104. The direction of polarization is aligned through a PS conversion element 105 by a mirror which separates light into p-polarized light and s-polarized light and a λ/2-plate which changes the polarization direction. The light that emerges from the PS conversion element 105 passes through a condenser lens 106 and the like. After that, a red-band light component is transmitted through a dichroic mirror DM101. Green- and blue-band light components are reflected by the dichroic mirror DM101. The blue-band light component is transmitted through a dichroic mirror DM102. The green-band light component is reflected by the dichroic mirror DM102. With this arrangement, the illumination light is separated into the light components in the red, green, and blue bands.
Each color light component becomes incident on a corresponding one of liquid crystal display elements 109R, 109G, and 109B and is modulated. These color light components are synthesized by a dichroic prism 111 and enlarged and projected onto a projection surface by a projecting lens 112.
Each color band will be described in more detail. The red-band light component transmitted through the dichroic mirror DM101 is changed in its optical path by 90° by a reflecting mirror M101, passes through a field lens 107R, becomes incident on an incident-side polarizing plate 108RI and liquid crystal display element 109R, and is modulated here.
The modulated red-band light component strikes an exit-side polarizing plate 110RO and dichroic prism 111 in this order. The optical path is changed by 90° by the dichroic prism 111. Then, the light component becomes incident on the projecting lens 112. The dichroic prism 111 is formed by bonding four prisms with adhesive such that it has an almost cross-shaped wavelength selection reflecting layer.
On the other hand, the green- and blue-band light components reflected and changed in their operation paths by 90° by the dichroic mirror DM101 become incident on the dichroic mirror DM102. The dichroic mirror DM102 has a characteristic for reflecting a green-band light component G. Hence, the green-band light component is reflected and changed in its optical path by 90° by the dichroic mirror DM102, transmitted through a field lens 107G, becomes incident on an incident-side polarizing plate 108GI and liquid crystal display element 109G, and is modulated here.
The modulated green-band light component strikes an exit-side polarizing plate 110GO and dichroic prism 111 in this order, passes through the dichroic prism 111, and becomes incident on the projecting lens 112.
The blue-band light component transmitted through the dichroic mirror DM102 passes through a condenser lens 113, relay lens 114, reflecting mirrors M102 and M103, and field lens 107B, becomes incident on an incident-side polarizing plate 108BI and liquid crystal display element 109B, and is modulated here.
The modulated blue-band light component strikes an exit-side polarizing plate 110BO and dichroic prism 111 in this order, is changed in its optical path by 90° by the dichroic prism 111, and becomes incident on the projecting lens 112.
The light components in the respective color bands, which are incident on the projecting lens 112 in the above-described manner, are projected onto the projection surface and displayed as an enlarged image.
In the above-described conventional projecting image display apparatus, a polarizing plate is normally formed by bonding a film-shaped polarizer b to transparent substrate a, as shown in FIG. 16, such that a predetermined polarizing characteristic can be exhibited. Both the incident-side polarizing plates and the exit-side polarizing plates are formed by bonding predetermined polarizers to transparent substrates, which have identical shapes independently of colors, for the respective color bands.
An incident-side polarizing plate absorbs light having a rotating polarization axis and converts the light into heat to align the polarization direction of light that becomes incident on a liquid crystal display element. In an exit-side polarizing plate, when the display color is black, the polarization axis of the polarizing plate is perpendicular to the amplitude of light emerging from a liquid crystal display element. Since all light components are absorbed and converted into heat, the heat load is very high.
If the aperture ratio of a liquid crystal display element is low, and the light amount of a lamp to be used is small, transparent substrates, e.g., glass substrates (the heat conductivity is about 1.2 W/(m·K)) having identical shapes suffice, as in the prior art.
Recently, 1.3 inches liquid crystal display elements have an aperture ratio of 60% even though the number of pixels is about 770,000. Some liquid crystal display elements improve the brightness of a projected image by increasing the power consumption of a lamp. Liquid crystal display elements themselves are also becoming compact.
The heat load changes for each color band and also depending on whether the polarizing plate is on the incident side or exit side. For example, when color purity of at least one of a plurality of color bands should be changed, the heat load on the incident- or exit-side polarizing plate of a specific color band increases. For this reason, the heat load on some incident- or exit-side polarizing plates increases, resulting in degradation in performance of the polarizing plate.
To solve the problem of heat load on a polarizing plate, sapphire whose heat conductivity (42 W/(m·K)) is about 40 times higher than that of a transparent glass substrate is used as a substrate to which a polarizer is bonded, as is proposed in Japanese Patent Application Laid-Open No. 11-231277.
However, sapphire is expensive. Use of sapphire is preferably avoided as much as possible from the viewpoint of cost. Especially, a 3-plate projecting image display apparatus as shown in FIG. 15 uses a total of six polarizing plates on the incident and exit sides. Since a plurality of sapphire substrates are normally required, the cost largely increases.
In addition, to increase the cooling efficiency by a cooling fan, the power consumption of the cooling fan increases, or noise becomes large.